The Tesla "D" that Elon Musk so provocatively tweeted about last week is actually an all-wheel-drive version of the Model S Sedan. There will be three versions, and each will carry the "D" designation, to distinguish them from the rear-wheel-drive Model S.

AWD will be a plus for Tesla's customers in the Northeast and in Northern Europe, to deal with bad weather.

The current performance version of the Model S — the P85 — will become the P85D and be capable of 0-60 mph in a blistering 3.2 seconds. That acceleration is right up there with supercars from Ferrari, Porsche, and Mercedes.

In addition to the "D" — and to be truthful, many Tesla observers speculated it was going to be all-wheel-drive — Tesla is introducing a cluster of driver-assist features. These include things like the car being able to read speed-limit signs and adjust its velocity, signals that make the car change lanes, and some familiar stuff, like lane-departure warnings.